When drilling a hole, drilling fluid or mud may be used to carry away cuttings, lubricate the bit, cool the bit, provide pressure control, and/or for other purposes as are known in the art. Drilling fluid or mud used in drilling of wellbores may be a mixture of water, clay, weighting material, and a few chemicals. Sometimes oil may be used instead of water, or a little oil is added to the water to give the mud certain desirable properties. Clay may be added to the mud so that it can keep the bit cuttings in suspension as they move up the hole. The clay may also sheath the wall of the hole. This thin veneer of clay is termed wall cake, and makes the hole stable so it will not cave in or slough.
The equipment in a typical drilling fluid circulating system may include a mud pump which takes in mud from the mud pits and sends it out a discharge line to a standpipe. The standpipe is a steel pipe mounted vertically on one leg of the mast or derrick. The mud is pumped up the standpipe and into a flexible, very strong, reinforced rubber hose called the rotary hose, or kelly hose. The rotary hose is connected to the swivel. The mud enters the swivel, flows down the kelly, drill pipe, and drill collars, and exists at the bit. It then flows with a sharp U-turn and heads back up the hole in the annulus which is the space between the outside of the drill string and wall of the hole. Finally, the mud leaves the hole through a steel pipe called the mud-return line and falls over a vibrating, screenlike device called the shale shaker. The shaker screens out the cuttings and dumps them into one of the reserve pits (the earthen pits excavated when the site was being prepared). The mud may be circulated over and over again throughout the drilling of the well.
Under some circumstances, it may be desirable to have a reverse circulation of drilling fluid, in which the fluid flows in a reverse manner to that described above, namely down the annulus and up the drill string. For example, reverse circulation may provide for an increased return velocity of the cuttings in the drill string, which could allow for a lower viscosity mud to achieve cuttings return; reverse circulation may provide for a better mechanism to sample the cuttings and/or mud from downhole; and/or reverse circulation may provide for a better mechanism for controlling downhole pressure.
U.S. Pat. No. 4,368,787 discloses an arrangement for drilling deviated wellbores, such as in extended reach drilling, which is particularly designed to reduce the chance of pressure-differential sticking of the drill string by removing the drilling cuttings from the wellbore bottom by reverse circulation of the drilling fluid using a pump powered by the cones of the rotary bit. The drill string is turned by a rotary, and as the drill string turns, the cones turn as they are rolled on the bottom of the hole. A power drive is taken off the bit cones, and powers a pump which pumps mud from the annulus, around and through the bit, and up the drill pipe. In this way, troublesome cuttings are kept out of the annulus, and the cuttings are more effectively removed by pumping up and out the drill pipe. U.S. Pat. No. 4,368,787 is herein incorporated by reference in its entirety.
There is a need in the art for improved systems and methods for reverse circulation drilling systems and methods. There is a need in the art for improved pumping systems to be used in reverse circulation drilling systems. There is a need in the art for higher volume pumping systems to be used in reverse circulation drilling systems. There is a need in the art for improved drill bit cleaning to be used in reverse circulation drilling systems.